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When giving a partial name to /buffer, e.g. "/buffer partialname", weechat will switch to the first buffer having a name which contains "partialname".
The full name could be irc.freenode.#partialname

When, for example, both "#partialname" and "partialname" buffers exist, "/buffer partialname" might not land you on "partialname" as you would expect, even though "partialname" matches more closely "partialname" than "#partialname" does.